Surface-mountable crystal resonator

ABSTRACT

A surface-mountable crystal resonator (100) is provided in the following manner. A first predetermined electrode pattern (105) and a second predetermined electrode pattern (201) are formed on a first major surface (104) and a second major surface (200), respectively, of a piezoelectric crystal substrate (101). Additionally, a first predetermined attachment electrode pattern (106), electrically coupled to the second predetermined attachment electrode pattern, and a second predetermined attachment electrode pattern (202), electrically coupled to the first predetermined attachment electrode pattern, are formed on a first attachment area (102) and a second attachment area (103), respectively. The first and second attachment areas include extensions (107) that, when mounted, allow a conductive adhesive (301), placed on a mounting substrate (300), to flow and establish electrical connections with the first and second predetermined attachment electrode patterns.

This is a continuation of application Ser. No. 08/109,192, filed Aug.19, 1993, and now abandoned.

FIELD OF THE INVENTION

The present invention relates generally to crystal resonators and, inparticular, to a surface-mountable crystal resonator.

BACKGROUND OF THE INVENTION

Crystal resonators are known to comprise a rectangular, piezoelectriccrystal substrate having two substantially planar, parallel majorsurfaces on opposite sides of the crystal substrate. Electrodes areformed on the major surfaces such that a voltage applied across theelectrodes causes the crystal substrate to resonate. In order forcrystal resonators to be surface-mountable, provisions must be made suchthat electrical connections can be established between both the top andbottom electrodes and a mounting substrate. It is often difficult and/orcostly, however, to establish electrical connections (typically throughthe use of solder or another electrically conductive adhesive) betweenthe top electrode and the mounting substrate.

One solution to this problem is to use an automated device, such as arobotic arm, to place a "top dot" of conductive adhesive on the crystalresonator. This operation wraps conductive adhesive from a conductivepad on the mounting substrate, around the crystal substrate, to the topelectrode such that a reliable electrical connection is created.Automated devices capable of such delicate operations are often veryexpensive, costing as much as one million dollars apiece, thus addingsubstantially to the overall cost of mounting each crystal resonator.

An alternative to this method is to fabricate the crystal resonator insuch away that a specialized automated device is not required toestablish electrical connection with the top electrode. It is known, forinstance, to place holes in the crystal substrate such that when thecrystal resonator is mechanically placed on the mounting substrate,conductive adhesive already positioned on the conductive pad is allowedto flow through the crystal substrate and establish an electricalconnection with the top electrode. A limitation of this method, however,is that the differing coefficients of expansion of the crystal substrateand the conductive adhesive can cause undo stresses on the crystalsubstrate when environmental conditions vary. These stresses, in turn,can adversely affect the performance of the crystal resonator.Therefore, a need exists for a surface-mountable crystal resonator thateliminates the need for additional automated mounting devices andovercomes the limitations of prior art solutions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a perspective view of a surface-mountable crystalresonator in accordance with the present invention.

FIG. 2 illustrates a side view of a surface-mountable crystal resonatorin accordance with the present invention.

FIG. 3 illustrates an alignment of a surface-mountable crystal resonatorin accordance with the present invention prior to mounting on a mountingsubstrate.

FIG. 4 illustrates a partial side view of a surface-mountable crystalresonator in accordance with the present invention after mounting on amounting substrate.

DESCRIPTION OF A PREFERRED EMBODIMENT

Generally, the present invention provides an apparatus for asurface-mountable crystal resonator. The surface-mountable crystalresonator is fabricated to include at least a first attachment area. Thefirst attachment area has at least one extension, such that, when thesurface mountable crystal resonator is placed on a mounting substrate,the extension displaces a conductive adhesive to establish an electricalconnection between an electrode of the resonator and an electrode of themounting substrate. With such a device, the resonator may be surfacemounted without the need for expensive placement equipment and withoutmounting holes in the resonator.

The present invention can be more fully described with reference toFIGS. 1-4. FIGS. 1 and 2 illustrate a surface-mountable crystalresonator (100) that includes a piezoelectric crystal substrate (101)having first and second major surfaces (200, 104) that are substantiallyparallel to each other and to first and second major axes (108-109), andsubstantially perpindicular to a third major axis (110). In a preferredembodiment, the crystal substrate (101) is an AT-cut strip blank asknown in the art. First and second attachment areas (102-103), parallelto either the first or second major axes (108, 109), are formed at eachend of the crystal substrate (101) using known techniques such as quartzetching or milling. Each attachment area (102-103) is fabricated toinclude at least one extension (107). The extensions (107) have apredetermined shape based on a predetermined cut of the crystalsubstrate (101) and the conditions in which the crystal substrate (101)is to be mounted. For instance, if the predetermined cut of the crystalsubstrate (101) is an AT cut, the predetermined shape of the extensions(107) can be a triangle having first and second extension surfacessubstantially perpendicular to each other and substantially at 45°angles with the first and second major axes (108-109).

Additionally, first and second electrodes (201, 105), each having apredetermined pattern, are formed on the first and second major surfaces(200, 104), respectively, thus forming an active area of resonance. Asis known, the active area of resonance, when excited with an electricalpotential, provides a mechanical vibration at the resonant frequency ofthe crystal (101). In a preferred embodiment, the predetermined patternof the first and second electrodes (201, 105) is a rectangular shape.

In order to provide electrical paths to the first and second electrodes(201, 105), first and second attachment electrodes (106, 202), eachhaving a predetermined shape, are formed on the second and first majorsurfaces (104, 200), respectively. In particular, the predeterminedshape is such that the first and second attachment areas (102-103),including the extensions (107), are substantially covered by the firstand second attachment electrodes (106, 202). As shown, the secondelectrode (105) and the first attachment electrode (106) areelectrically coupled. Additionally, the first electrode (201) and thesecond attachment electrode (202) are electrically coupled. Note thatthe first and second electrodes (105, 201) and the first and secondattachment electrodes (106, 202) are formed on their respective surfacesusing know metallization and/or etching techniques. Having formed thesurface-mountable crystal resonator (100) in accordance with the aboveteachings, a method of mounting such a resonator is further describedwith the aid of FIGS. 3 and 4.

FIG. 3 illustrates an alignment of the surface-mountable crystalresonator (100) prior to mounting on a mounting substrate (300). A beadof conductive adhesive (301) is deposited at a first conductive area onthe mounting substrate (300). In a preferred embodiment, the conductiveadhesive (301) is either a conductive epoxy or solder. The resonator(100) is then placed such that the first attachment area (102) and thefirst attachment electrode (106) are above the conductive adhesive(301). The resonator (100) is then lowered such that the firstattachment area (102) is placed in the conductive adhesive (301). Theconductive adhesive (301) flows through the first attachment area (102)and establishes an electrical connection between the first attachmentelectrode (106) and the first conductive area. The predetermined shapeof the extensions (107) allows the flow of the conductive adhesive (301)to wrap around the first attachment area (102) and make an electricalconnection with the first attachment electrode (106). It is understoodthat the second attachment area (103) and the second attachmentelectrode (202) may be simultaneously placed over a second conductivearea (not shown) having a bead of conductive adhesive. Thus, when theresonator (100) is lowered, the conductive adhesive can establish anelectrical connection between the second attachment electrode (202) andthe second conductive area. The fact that the second attachmentelectrode (202) directly faces, in this example, the conductiveadhesive, virtually guarantees a proper electrical connection. Theadvantages provided by the present invention are more clearly seen inFIG. 4.

FIG. 4 illustrates a side view of the resonator (100) after it has beenproperly mounted. The conductive adhesive (301) has established contactwith the first attachment electrode (106) by flowing through theextensions (107) thus eliminating the need for another operation toelectrically connect the conductive adhesive (301) to the firstattachment electrode (106). By identically establishing the first andsecond attachment areas (102, 103) and their respective first and secondattachment electrodes (106, 202) on opposite sides of each end of thecrystal substrate (101), either the first or second major surface (200,104) may be mounted facing the mounting substrate (300).

The present invention provides an apparatus for a surface-mountablecrystal resonator. With such an apparatus, electrical connections can bemade between electrodes facing away from the mounting substrate andconductive areas found on the mounting substrate without the use of aseparate manufacturing operation. Furthermore, the present inventionovercomes the limitations of the prior art in which a hole is etchedthrough the crystal substrate in order to aid the creation of electricalconnections. These problems are eliminated through the use of extensionswhich allow conductive adhesive to flow throughout those areas requiredto establish an electrical connection.

What is claimed is:
 1. A surface-mountable crystal resonatorcomprising:a piezoelectric crystal substrate having a first majorsurface, a second major surface, and a first attachment area, whereinthe first major surface and second major surface are substantiallyco-planar separated by thickness of the crystal substrate and areparallel to a first major axis and a second major axis and perpendicularto a third major axis, wherein the first major axis, the second majoraxis, and the third major axis are substantially perpendicular to eachother, and wherein the first attachment area is substantially parallelto the first major axis and includes at least two extensions, each ofthe at least two extensions comprising:a first extension surface,wherein the first extension surface is planar and substantially at 45degree angles with respect to the first major axis and the second majoraxis and substantially parallel with respect to the third major axis;and a second extension surface, wherein the second extension surface isplanar and substantially at 45 degree angles with respect to the firstmajor axis and the second major axis and substantially parallel withrespect to the third major axis, and wherein the first extension surfaceand the second extension surface are substantially perpendicular; afirst predetermined electrode pattern deposited on the first majorsurface; a second predetermined electrode pattern deposited on thesecond major surface, wherein the first predetermined electrode patternand the second predetermined electrode pattern form an active area ofresonance; and a first predetermined attachment electrode patterndeposited on the first attachment area, wherein the first predeterminedattachment electrode pattern is electrically coupled to the secondpredetermined electrode pattern.
 2. The surface-mountable crystalresonator of claim 1 further comprises:a second attachment area, whereinthe second attachment area is substantially parallel to the firstattachment area and includes the at least one extension having thepredetermined shape.
 3. The surface-mountable crystal resonator of claim2 further comprises:a second predetermined attachment electrode patternthat is deposited on the second attachment area, wherein the secondpredetermined attachment electrode pattern is electrically coupled tothe first predetermined electrode pattern.
 4. A surface-mountablecrystal resonator comprising:an AT-cut piezoelectric crystal substratehaving a first major surface, a second major surface, a first attachmentarea, and a second attachment area, wherein the first major surface andsecond major surface are substantially co-planar separated by thicknessof the crystal substrate and are parallel to a first major axis and asecond major axis and perpendicular to a third major axis, wherein thefirst major axis, the second major axis, and the third major axis aresubstantially perpendicular to each other, and wherein the firstattachment area and the second attachment area are substantiallyparallel to the first major axis and each include at least twoextensions, each of the at least two extensions comprising:a firstextension surface, wherein the first extension surface is planar andsubstantially at 45 degree angles with respect to the first major axisand the second major axis and substantially parallel with respect to thethird major axis; and a second extension surface, wherein the secondextension surface is planar and substantially at 45 degree angles withrespect to the first major axis and the second major axis andsubstantially parallel with respect to the third major axis, and whereinthe first extension surface and the second extension surface aresubstantially perpendicular: a first predetermined electrode patterndeposited on the first major surface; a second predetermined electrodepattern deposited on the second major surface, wherein the firstpredetermined electrode pattern and the second predetermined electrodepattern form an active area of resonance; a first predeterminedattachment electrode pattern deposited on the first attachment area,wherein the first predetermined attachment electrode pattern iselectrically coupled to the second predetermined electrode pattern; anda second predetermined attachment electrode pattern deposited on thesecond attachment area, wherein the second predetermined attachmentelectrode pattern is electrically coupled to the first predeterminedelectrode pattern.